Integrated circuit technology relies on transistors to formulate vast arrays of functional circuits. The complexity of these circuits requires the use of an ever increasing number of linked transistors. As the number of transistors required increases, the integrated circuitry dimensions shrink. It is one objective in the semiconductor industry to construct transistors and other discrete devices which occupy less surface area on a given silicon chip/die. At the same time, the semiconductor industry seeks to increase the speed and power offered by integrated circuits. One approach to the latter challenge is through the development of improved methods for electrically connecting and packaging circuit devices which are fabricated on the same or on different silicon chips.
Ideally, we would like to build a computing system by fabricating all the necessary integrated circuits on one wafer or chip, as compared with today's method of fabricating many chips of different functions and packaging them to assemble a system. A true “system on a chip” would greatly improve integrated circuit performance and provide higher bandwidth. Unfortunately, it is very difficult with today's technology to implement a truly high-performance “system on a chip” because of vastly different fabrication processes and different manufacturing yields for the logic and memory circuits.
As a compromise, various “system modules” have been introduced that electrically connect and package circuit devices which are fabricated on the same or on different semiconductor chips. These began with simply stacking two semiconductor chips, e.g. a logic and memory chip, one on top of the other in an arrangement commonly referred to as chip-on-chip (COC) structure. Chip-on-chip structure most commonly utilizes micro bump bonding technology (MBB) to electrically connect the two chips. Several problems, however, remain inherent with this design structure. One serious complication includes the heating which occurs most seriously in connection with a logic chip such as a microprocessor. In high-performance microprocessors, where CPUs are running at 500 MHz and dissipating up to 85 watts of power, cooling becomes a crucial issue.
Usually, the cooling of such a package is accomplished by forced air. In certain applications, however, forced air cooling is not feasible or practical. Examples of such applications include computers to be used in outer space, in a vacuum environment on earth, or in clean rooms where air circulation is not desirable. For these and other instances, a different method of cooling is required. Another cooling method includes liquid cooling, such as the forced water cooling used in the thermal conduction modules of IBM main frame computers and forced freon cooling used in Cray supercomputers. Still, liquid cooling methods can also prove too bulky, costly, and not easily adapted for use in compact high-performance integrated circuit systems, e.g. portable devices.
Thus, it is desirable to develop an improved structure and method for cooling high performance integrated circuit systems. Additionally, the improved structure and method should accommodate a dense integration and packaging for semiconductor chips, e.g. logic and memory chips.